Last summer the Pak Brake stopped working on my 1993 U-280. The light in the switch comes on and the valve opens and closes normally. It does not down shift or actuate the valve on the exhaust when you let off the accelerator pedal. I'm pretty certain the switch on the accelerator control on the engine plays a role in this system and I'm wondering if anyone has a wiring diagram for the Pak Brake or has any suggestions. Thanks in advance!
Correct. If the signal from the throttle switch doesn't indicate CLOSE THROTTLE, the exhaust brake will not activate.
Since the Allison is not downshifting, the issue is "upstream" of the Allison, since it is the first thing in the electronic "chain" that engages the exhaust brake.
Ian,
Always nice to hear from other U280 owners. I see from your signature that your coach has AquaHot. I would imagine that is a very unusual option for that model year.
We have an exhaust brake on our U280, but from a different manufacturer, so I don't have a specific answer to your wiring question. To operate our exhaust brake, there is a switch on the wall next to driver seat that turns the brake ON, and a pressure sensing pad on the throttle pedal. When turned ON, if I let off all the pressure on the throttle pedal the exhaust brake closes. If I apply ANY pressure to the throttle pedal, the exhaust brake opens.
I did find the Forum thread linked below. If you read through the whole thread, you may find some helpful info on your PacBrake.
94 U280 Pac Brake Switch (https://www.foreforums.com/index.php?topic=35880.0)
Pacbrake:Exhaust Brakes (https://pacbrake.com/exhaust-brakes.html?Sort_By=disp_order&Per_Page=15&product_country=ALL&product_country=US)
Thanks Brett. I'll pull the connector to the switch and put a meter on it.
Thanks Chuck. The links are helpful!